RFR: JDK-8170884 Clean up post-jlink file copying to the images

[Magnus Ihse Bursie]

When jlink was removed, the structure of how we copied "extra" files to 
the image was changed. In fact, there is no longer any such copies in 
the OpenJDK build, so any code related to this can and should be removed 
from the open build.

Bug: https://bugs.openjdk.java.net/browse/JDK-8170884
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8170884-clean-up-README-copying/webrev.01

/Magnus